Asea Brown Boveri Ab

Ingvar Niemi

Goran Engdahl

Gunnar Molund

An electric switching device according to the invention comprises two fixed contacts and one movable contact, referred to jointly as the main contact system. The main contact system is located in an oil-insulated cavity enclosed in a housing. In its direction of movement, the movable contact has an extension in the form of a shaft. The shaft is formed with a hydraulic piston by which the movable contact is operated. The hydraulic piston is surrounded by a cavity in which a piston cavity is formed on each side of the hydraulic piston. The piston cavities are oil-filled. The movement of the shaft is determined by an electrically controlled directional valve. The directional valve receives signals as to whether the electric switching device is to be opened or closed. At a given signal, the directional valve distributes a high pressure to the piston cavity that is to be enlarged. The electric switching device can be provided with an auxiliary contact mechanism which can be placed either in the fixed contacts and/or in the movable contact. The electric switching device is provided with a bistable mechanism comprising wedge-shaped pistons biased by means of springs. The wedge-shaped pistons, in case of drop-out of pressure, lock the movable contact in the existing position via the shaft.

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Vaster.ang.s, Sweden

Ingvar Niemi